1. Field of the Invention
The present invention relates to diagnostic assays for analytes in a liquid sample. In some embodiments, methods and devices for the detection of an analyte in a body fluid using a plurality of species-specific antibodies are provided.
2. Description of the Related Art
Many types of ligand-receptor assays have been used to detect the presence of analytes in body fluids such as saliva, urine or blood. These assays typically involve antigen-antibody reactions, synthetic conjugates comprising enzymatic, fluorescent, or visually observable tags, and specially designed reactor chambers. In most of these assays, there is a receptor (e.g., an antibody) specific for the selected analyte (e.g., antigen), and a means for detecting the presence and/or amount of the antigen-antibody reaction product. Although some commercially available tests are designed to make a quantitative determination, in many circumstances all that is required is a qualitative indication (e.g., positive/negative). Examples of such qualitative assays include blood typing, pregnancy testing, ovulation prediction and many types of urinalysis. For these tests, visually observable indicia, such as the presence of agglutination or a color change, are preferred.
Diagnostic assays should generally be very sensitive because of the often low concentrations of analytes of interest present in a test fluid. False positives can be problematic, particularly with agglutination and other rapid detection methods such as dipstick and color change tests. Because of these problems, sandwich assays which use metal sols or other types of colored particles have been developed that rely on the interaction between avidin and biotin-tagged antibodies. For example, in some commercially available pregnancy tests, an antibody-antigen sandwich complex comprising a colloidal gold-labeled anti-hCG antibody and an anti-hCG biotin-labeled antibody is used.
Because the above disclosed assays and methods enable the formation of antibody-antigen sandwich complexes in the liquid phase of an assay prior to the test line, they allow for more time for antigen recognition and binding to occur. These assays and methods therefore have greater sensitivity and discrimination for analytes of interest, resulting in greater reproducibility, sensitivity, and avoidance of false positives. Although such advances have improved these types of assays, further improvements in reliability and ease of manufacture are desirable.